Objective: To determine the frequency of dissociation and childhood trauma among obsessive-compulsive patients by comparing with healthy controls. Methods: This study comprises of a group of 50 patients attending to Hamidiye Etfal Training and Research Hospital Psychiatric Outpatients Department who had been diagnosed as obsessive-compulsive disorder according to DSM-5 and a control group of 50 participants with no psychiatric diagnosis. The groups were collected between September 2014 and January 2015. SCID-I, SCID-D, Dissociative Experiences Scale (DES), Childhood Trauma Quetionnaire (CTQ-28) and a short instrument gathering qualitative information about childhood traumatic experiences were administered to all attendees with a sociodemographic form. Results: Mean DES and CTQ-28 total scores were determined as significantly different between OCD and control groups. In the OCD group, the percentage of existence of at least one type of dissociative disorder was 14%. In CTQ-28 subscales scores, there were significant differences between OCD and control groups for emotional neglect, emoti-onal abuse and physical abuse. Moreover, 70% of the OCD group has had at least one type of childhood trauma. In childhood trauma subscales, there were also significant differences between OCD and control groups for at least one type of childhood trauma, emotional neglect, emotional abuse, physical abuse and sexual abuse. Discussion: Findings of significant differences between OCD patients and healthy controls according to dissociation and child-hood trauma, 14% of at least one type of dissociative disorder and 70% of at least one type of childhood trauma in OCD patients are main findings of this study. Our study differentiates from other studies in our country that its having a control group. Considering above findings, it has revealed that because of its probable effects on the diagnosis and treatment, co-existence of OCD with dissociation and childhood trauma is needed to be taken account. [Anadolu Psikiyatri Derg 2019; 20(3.000): 287-295]